The present invention relates to a method for operating a communication system, particularly in order to reduce power consumption.
Possible communication systems comprise a plurality of communication units or nodes, usually a central instance (also called a “master” or “coordinator”) and a commonly used communication medium (also referred to as a “common transmission medium” or “shared medium”).
A fundamental problem in a communication system of this type is the control of access to the shared medium, since, with simultaneous use of the same resources by different nodes, a successful (i.e. error-free) transmission is impossible. There are a multiplicity of different degrees of freedom and possible forms, and also many different directions of optimization, for example in terms of throughput, fairness, real-time capability, etc.
A distinction can generally be made between contention-based and coordinated media access methods.
In the case of contention-based methods, it may essentially occur that two or more nodes wish to access the shared medium simultaneously and transmit corresponding data, which then results in a collision on the common transmission medium. Examples of this type of method are (Slotted) ALOHA, Carrier Sense Multiple Access (CSMA) and CSMA with collision detection (CSMA/CD), used, inter alia, in the Ethernet variants 10BASE5 and 10BASE2.
Unlike contention-based methods, in coordinated media access methods no collisions due to simultaneous access should occur in the error-free case. Media access can be coordinated statically, such as e.g. in the case of static time division multiplex methods in which each node is allowed exclusively to use the shared medium periodically for a certain time for transmission. This can be done, for example, using a statically defined schedule which is known to all nodes, in conjunction with a time synchronization of all nodes. Alternatively, the coordination can be implemented using a control by a central instance, such as, for example, in the case of a conventional polling method. In addition, however, a distributed coordination is possible, as used e.g. in methods such as “Token Ring” or “Token Bus”.
Reducing the energy consumption of individual nodes in a communication of this type is generally a major concern. This conventionally applies, in particular, to wireless communication systems (e.g. wireless sensor networks), since individual nodes are often battery-operated here or even operate energy harvesting, i.e. they obtain their energy from the environment itself.
This obviously applies in principle to wired systems also, for example if individual nodes are to be supplied with power via the communication line or generally power consumption is to be minimized e.g. in order to reduce operating costs.
The fundamental idea of most approaches is normally that a node switches back and forth between a normal operating mode in which it is fully functional and one or more special sleeping modes, also generally referred to below as standby mode, with restricted functionality. A node in a sleeping mode could thus disable all functions, apart from a timer for switching back to the normal operating mode, including all communication functions, so that the node is not operable in this mode.
Different possible approaches are, for example, as follows:
A node can be woken up, for example, by means of an external triggering by applying a specific (electric) signal. A possible application for this is e.g. a switch which must transmit a corresponding mode change to a different mode (e.g. a gateway or central controller) only in the event of changes in the switching state.
A switchover between operating modes periodically in a fixed pattern is one option, particularly for communication systems in which, for example, a specific beacon frame is transmitted periodically, after which transmissions can take place in a targeted manner, or with which pending transmissions can be announced, or for communication systems with a fixed timing pattern in which e.g. fixed-size timeslots are defined and at least one timeslot is allocated to each node. In this case, a node could thus readily be in sleeping mode outside its timeslots.
From DE 10 2011 084 740 A1, for example, a method for data transmission is known in which a data packet is divided up into a header and a payload for energy reduction, wherein the header is transmitted in a less complex mode than the payload.
The object of the present invention is to provide a communication method for a communication system which enables flexible switchovers between operating modes and long time durations in an energy-saving mode, and which has the most efficient possible energy consumption.